Due to the rapid development of the electronic and information industries in recent years, the new generation of semiconductor production processes demand the epoxy resin to have a high I/O (Input and Output Count) modulus, high heat resistance, high flowability, high physical properties, etc. Therefore, the studies on how to improve the flexibility and heat resistance of the epoxy resin become another essential field of research. The structure of a siloxane compound has properties such as good thermal stability and anti-oxidation property, good air permeability and electrical insulation property, maintaining softness, elasticity and flowability at a low temperature, good weather resistance, and low stress formation, etc. Therefore, such a structure is helpful to the improvement of flexibility and the reduction of stress formation.
In 1996, Chun-Shan Wang et al. [T. H. Ho, C. S. Wang, polymer, 37, 2722(1996)] produced thermoplastic polyurethane (TPU) by reacting various siloxane compound monomers of OH-terminated polydimethyl siloxane with isocyanate-containing monomers such as MDI or TDI in room temperature using dibutyltindilaurate-T12 as the catalyst. The reaction forms a thermoplastic polyurethane (TPU) with the main chain of which containing siloxane. The TPU of various structure is blended with an o-cresol formaldehyde novolac epoxy resin and then cured at 150.degree. C. and 50 kgr/cm.sup.2 for one hour, and at 180.degree. C. and 210.degree. C. for two and three hours, respectively. The results indicate that the cured article has a higher thermal resistance and a higher Thermal Shock Cycling Test value thereby improving the defects in the thermal resistance and the existence of internal stress existed the epoxy resin molding formulation for IC packaging.
The curing of an epoxy resin at a high temperature will cause the formation of a residual internal stress and brittleness. Relatively, polysiloxane has a lower degree of stress formation and a better flexibility. Therefore, the use of polysiloxane in improving the flexibility of epoxy resin has received a wide attention in the industry. However, there is a large difference in the solubility parameter between the polysiloxane and the epoxy resin thereby causing a severe phase separation and a non-uniform distribution of the polysiloxane in the epoxy resin. There are a wide variety of epoxy resins and their hardeners; and the reaction mechanisms thereof vary, as well. Therefore, the addition of a polysiloxane into any epoxy resin curing system will not unanimously achieve the property-modifying effects. The predominant factor affecting the improvement of flexibility is the improvement of the compatibility between the polysiloxane and the epoxy resin. Therefore, the increase of the molecular attractions between the polysiloxane and the epoxy resin can achieve this effect; and the formation of the hydrogen bonding is the most effective method in increasing the attractive force between two molecules.
The objectives of the present invention are to provide a polysiloxane urethane modifier and the use of the modifier in improving the flexibility of the epoxy resin and toughening the epoxy resin by grafting the modifier to an epoxy resin.